Carbonated beverages range in variety from carbonated water, knows as soda water or sparkling water, to a carbonated water flavored with natural or artificial flavors such as orange, lemon-lime, cola, and many more.
The amount of carbon dioxide gas dissolved into these products is usually referred to as Volume of CO.sub.2 per Volume of Liquid. The higher the volume of CO.sub.2 per unit Volume of Liquid, the greater the sparkle and effervescence of the beverage. Although the desirable level of carbonation in a beverage is a matter of personal preference, packaged soft drinks are usually made with 3.5 to 4.0 volumes of carbon dioxide for colas, 4.0 to 5.0 Volumes of CO.sub.2 for seltzers and soda water and generally less that 3.0 volumes for orange flavor. One of the disadvantages of packaged carbonated beverages is that the carbonation level is fixed and not available at different levels to suit different personal tastes.
Other disadvantages of packaged carbonated beverages include the unnecessary cost of packaging and transportation of a product that is comprised essentially of water and the cost of disposal or recycling of the package. Still further is the problem that once the pressurized beverage container is open to the atmosphere, the beverage left unconsumed and unpressurized tends to lose carbonation and go flat thus wasting the unconsumed portion.
Several products have been developed to overcome the above noted problems and make possible the preparation of carbonated beverages in the home.
One such product is described in Norwegian Patent No. 52210. This device uses a high pressure metal cylinder to supply carbon dioxide to carbonate water. Disposable high pressure gas cylinders are sufficiently expensive to offset any price advantage sought through the use of a portable carbonation device. In addition, they are inconvenient to procure and present a waste disposal problem with the empty cylinder.
Furthermore, in operation, this device does not produce acceptable carbonation with a practical waiting period because a pressure equilibrium between the CO.sub.2 cylinder and carbonate bottle is established soon after the CO.sub.2 cylinder is connected to the bottle. This pressure equilibrium prevents further flow of gas from the cylinder until the CO.sub.2 is gradually absorbed by the water.
U.S. Pat. No. 4,719,056 (Scott) also discloses a method of carbonating water with propellent carbon dioxide packaged in a high pressure metal cylinder. The method for dissolving carbon dioxide gas into water through use of high speed rotating vanes is a very effective means to achieve rapid carbonation at high CO.sub.2 Volume levels; however, this device has the disadvantage of the cost of a source of rotating mechanical motion. A further disadvantage is the requirement of a rotary seal on the mixing shaft to separate the pressurized carbonation chamber from atmospheric pressure. Rotary seals are known to be prone to leakage and premature failure especially when they are used at the elevated pressures specified.
Home carbonating devices requiring the use of CO.sub.2 gas packaged in gas cylinders as described by U.S. Pat. No. 4,719,056 (Scott) and U.S. Pat. No. 4,251,473 (Gilbey) are not practical for mass distribution for several reasons. If the cylinders are single use and, therefore disposable, the cost of the carbon dioxide and the cylinder spread over the quantity of carbonated beverage they produce is significantly higher than the cost of an equivalent quantity of packaged carbonated beverage. If the cylinders are the reusable type, the cost of the cylinder can, of course, be divided by the number of times it is refilled; however, refilling a CO.sub.2 gas cylinder is inconvenient and expensive because the cost of labor to perform the refilling is far greater that the cost of the gas itself. Complicating this situation further is the limited number of CO.sub.2 refill stations, since even in advanced economic societies, CO.sub.2 gas refilling stations are generally limited to serving commercial and industrial users. In order to overcome the cost and inconvenience of gas cylinder as the source of carbon dioxide for a home carbonator, several devices that derive the carbonating gas from a chemical reaction have been developed.
One such apparatus described in U.S. Pat. No. 4,347,783 (Ogden) derives the carbon dioxide from a reaction of yeast and sugar or, alternatively, from a chemical reaction of an edible acid with a carbonate in an aqueous solution. One problem with the device is that it does not produce a satisfactory level of carbonation, i.e. at least 3 Volumes of CO.sub.2 or more, in a reasonable period of time.
U.S. Pat. No. 4,040,342 (Austin) discloses a gas generating chamber with a gas conduit extending into a carbonating chamber. After the chemical reaction is activated, the carbon dioxide flows into the carbonating chamber and carbonates the liquid contained therein. There are several limitations and problems with this device.
First, the time required to carbonate the liquid to 3 or more Volumes of CO.sub.2 is fifteen minutes or greater. This is because the process of dissolving carbon dioxide into liquid occurs in two mechanisms; one quite rapid and the other quite slow. Some of the gas dissolves into the liquid as it bubbles to the surface and fills the head space of the carbonation tank. This CO.sub.2 solution process occurs quite rapidly though it is, of course, dependent upon the rate of the chemical reaction producing the CO.sub.2. Pressurized CO.sub.2 in the head space acting upon the surface of the liquid is the other gas absorption mechanism. This absorption rate is slow because of the fixed interfacial exposure area between the CO.sub.2 and the liquid. If this interfacial exposure area could be increased by agitation or by turbulent mixing as is taught by U.S. Pat. No. 4,719,056 (Scott) then CO.sub.2 absorption would occur far more rapidly.
The other problem is the likely occurrence of transfer of some of the salt by-products of the CO.sub.2 generation reaction into the liquid to be carbonated.
The reaction of edible acids (such as citric) with carbonates (such as sodium bicarbonate) in an aqueous solution is an endothermic reaction. When the reaction is first initiated, therefore, it is at its maximum temperature and its fastest reaction rate. In addition, the maximum amount of fuel for the reaction is present when it first begins. Therefore, during its initial stages the reaction produces considerable foaming and surface effervescence releasing a mist of reactant salt spray into the carbon dioxide gas being generated. This salt mist enters the carbonation chamber and ultimately the liquid being carbonated.
If hot water is used as the reactant water, the reaction rate is accelerated even further and salt contamination increases further.
U.S. Pat. No. 4,636,337 (Gupta) shows an apparatus that carbonates water rapidly with carbon dioxide generated in a reaction vessel from chemicals contained in a package. Water is added to the vessel containing the package and dissolves the package or package glue seams to expose the chemicals and react with them producing carbon dioxide gas.
One problem with this approach is that it requires a special water permeable (or soluble) package that will open and react with water after a delay time of immersion in the water. However, this delay time will vary according to the temperature of the reactant water and may begin before the user attaches the vessel to the carbonating apparatus; thus creating a potentially hazardous condition. Also, the possibility of reaction activation prior to attaching the vessel to the apparatus is always present if the user is distracted or delayed after adding water to the vessel containing the chemical package.
Further, the water soluble package containing the CO.sub.2 producing chemicals must itself be contained in another package to prevent deterioration of the package and the chemicals contained therein by atmospheric humidity or exposure to water. As a result, there is a double packaging cost.
Finally, if the reactant water temperature is too high, some foaming and effervescence will occur in the reaction vessel causing reactant salt mist to enter the CO.sub.2 gas conduit and contaminate the beverage therein.
For improved consumer convenience, the direct carbonation of premixed beverage is more desirable than the carbonation of unflavored water to which a flavoring must be added with each serving of soda water dispensed. With the Austin apparatus, U.S. Pat. No. 4,040,342, direct carbonation of premixed beverages would not be practical because premix flavoring syrups typically contain sugar and other ingredients that sufficiently alter the surface tension of the water syrup mix to cause the mixture to foam profusely; thus expelling much of the carbonation as it is dispensed from the pressurized carbonation vessel into a receptacle at atmospheric pressure. Most commercial soda fountains meter and mix flavoring syrup into the carbonated water after the water is dispensed from the pressurized carbonation vessel; therefore, when the syrup and carbonated water are combined, they are at atmospheric pressured (a process know in the industry as "post mix") and the foaming problem is avoided.
While the Gupta device does allow direct carbonation of premixed beverages, it does not solve the problem of the loss of carbonation in the unconsumed beverage portion left in the unpressurized container.